Sources close to the star described the health scare as “serious”, suggesting he is unlikely to be back to full strength for at least several weeks.

An insider said: “Jeremy has never been too concerned with clean living but this has knocked him for six.

“He’s told friends not to expect to hear too much from him over the next few weeks which is very unlike him, and obviously his family are concerned.

“Inevitably people close to him are saying it’s time to think about the way he looks after himself – cutting back on the booze and fags – but he’s never been one to take that sort of guidance on board.

“This might be a turning point.”

Clarkson was enjoying a break from filming his big budget Amazon Prime show when he headed abroad for the holiday – but had been expected to go straight back to work on his return.

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Sources say he now plans to take a period of respite instead and won’t return until he’s fully fit.

A spokeswoman for The Grand Tour said last night: “Jeremy Clarkson was admitted to hospital on Friday morning during a family holiday in Spain, and is being treated for pneumonia.”

He yesterday posted a photograph which showed medical tubing coming out of his arm on Instagram, and in a message to his friend Jemima Goldsmith on Twitter said he was currently “in a wheelchair, connected up to tubes, in a hospital”.

Two years ago the 57-year-old Sun columnist revealed he suffered a major health scare when doctors discovered a lump on his tongue, which experts told him was “probably cancer”.

Clarkson, Hammond and May are back in the first teaser for series 2 of The Grand Tour on Amazon Prime

The shock diagnosis, which was later found to be incorrect, came two days before an incident in which he punched a Top Gear producer which saw him axed by the corporation.

He described the incident as his "most stressful day" and explained: "Two days before the 'fracas' I'd been told, sternly, by my doctor that a lump on my tongue was probably cancer and that I must get it checked out immediately.

"But I couldn't do that. We were in the middle of a Top Gear series. And Top Gear always came first."

He has also admitted being "atrociously out of shape", says he has smoked "half a million cigarettes" and has been on the receiving end of countless medical warnings about his lifestyle.